Microsystem component and method for gluing microcomponents to a substrate

ABSTRACT

A method for gluing microcomponents to a substrate ( 1 ) during the production of microsystem components includes the steps of applying a reactive or non-reactive hot melt type adhesive ( 5 ) to the microcomponent ( 18 ) and/or the substrate ( 1 ), heating the hot melt type adhesive ( 5 ), and placing the microcomponent ( 18 ) onto the substrate ( 1 ). The hot melt type adhesive ( 5 ) is on the contact surfaces between the microcomponent ( 18 ) and the substrate ( 1 ) during and after gluing.

The invention relates to a method for gluing microcomponents to asubstrate in the production of microsystem components.

The invention further relates to a microsystem component having at leastone microcomponent glued to a substrate.

In many cases in microsystems technology, electronic, electromechanicalor purely mechanical microcomponents are glued to a substrate. Theprecision which is needed here, the low bond areas, and the need toautomate the joining operation pose a particular problem here.Microcomponents are conventionally glued using viscous adhesives as one-or two-part systems which have a specific potlife within which theadhesion properties are retained and the bonding operation can beimplemented. Viscous adhesives, moreover, have a specific cure timewhich the adhesive needs in order to ensure a stable bond.

Publications U.S. Pat. No. 6,126,765, US 2003/0029724 A1, and WO98/45693 describe methods of this kind for bonding microstructures usingviscous hotmelt adhesives.

The potlife ought to be as long as possible, in order to allow rationaljoining of microcomponents by extensive application of the adhesive tothe substrate, and subsequent joining of a multiplicity ofmicrocomponents to the substrate in a time required for the operation.On the other hand, the pot life and cure time should be as short aspossible, so that the adhesive bond cures immediately after the joiningoperation and the microcomponents are not displaced on the substrate.These two contrary boundary conditions are almost impossible toreconcile with one another. A further complicating factor is the lowthickness of the film of adhesive that is required in microsystemstechnology, in the μm range, which is different from macroscopicbonding.

DE 198 50 041 A1 describes a microtechnological bonding method ofproducing an adhesive bond using a liquid or pasty hotmelt adhesivewhich has at least a viscosity such that it can be placed as a string ofadhesive with a defined cross section on one of the adherends. Thegluing effect is only developed under specific externalconditions—heating of the adhesive, for example—so that the string ofadhesive can be displaced, owing to the as yet absent or minimaladhesion tendency. However, this may result in the desired bond areabeing only partly wetted with the required amount of adhesive, whichleads to a significant reduction in the quality of the joint.

DE 37 39 333 A1 describes a method of producing hotmelt adhesive bondsthat uses a laser as its heat source. The method envisages treating thereverse face of the adherend wafers by coating them with a hotmeltadhesive solution or with an adhesive varnish in a varnish spin-coatingunit or laminating them by means of an adhesive sheet, using a sheetironing unit. The wafers are subsequently sawn in the usual way, and theindividualized chips are dried. The chips are then lifted cyclically andsimultaneously from the wafer and fixed in pairs using the laser. Theenergy of the laser beam serves here to melt the adhesive in order toproduce the joining of the adherends.

It is an object of the invention, therefore, to provide an improvedmethod of gluing microcomponents to a substrate for producingmicrosystem components that allows rational joining of a multiplicity ofmicrocomponents individually in succession or, preferably, in one stepand prevents displacement of the microcomponents after they have beenapplied to the substrate, while taking into account the high precisionrequirements of Microsystems technology.

This object is inventively achieved with the generic method such thatpulverulent hotmelt adhesive is applied areally to the surface of thesubstrate or microcomponent, selected bondsites are incipiently meltedby local heating by means of irradiation of the selected bondsitesthrough a focusable heat source, and the powder layer not incipientlymelted is removed. This is then followed by the adhesion of the at leastone microcomponent to the substrate by application of themicrocomponents to the substrate and further heating of the assembly.

Reactive or nonreactive hotmelt adhesives are known in principle fromthe macro technology. In contradistinction to the viscous adhesives,bonding takes place immediately during cooling, without a cooling time,when the hotmelt adhesive has been heated to above the meltingtemperature. Depending on the hotmelt adhesive, the adhesive bond isreversible or irreversible. In the case of reactive or near-crosslinkinghotmelt adhesives, the adhesive bond is not reversible as soon as thereaction or near-crosslinking has been initiated. With a reversibleadhesive bond, the microcomponent can be detached again followingheating above a specific temperature. Nevertheless, both reversible andirreversible adhesive bonding ensure an attachment of the microcomponentto the substrate with which the microcomponent no longer undergoesdisplacement, not even over tiny distances in the μm range.

Hotmelt adhesives are adhesives which melt on exposure to heat and, onsolidifying, form the adhesive bond. Examples of customary hotmeltadhesives include mixtures of ethylene-vinyl acetate copolymers,polyamides or saturated polyesters with additives such as resins,plasticizers, stabilizers or fillers.

Reactive adhesives are to be seen in contradistinction to hotmeltadhesives, and set by chemical reaction. In this case, however, theaforementioned problem of potlife and setting time arises. Furthermore,incipiently dissolving adhesives are known which incipiently dissolvethe surfaces to be bonded, so that the bond occurs after themacromolecules have undergone diffusion and the solvent has evaporated.Here too, the reaction time is too long. General-purpose adhesiveslikewise set by evaporation of solvent.

The reactive or nonreactive hotmelt adhesives are also to be seen incontradistinction to conventional pressure-sensitive adhesives, which,as permanent adhesives, commonly based on rubber, adhere under lowpressure but tend to creep under permanent load. Also unsuitable arecontact adhesives, which must be applied to both adherend surfaces, thebond in this case occurring, after preliminary drying, by means ofbrief, forceful compression.

Reactive or nonreactive hotmelt adhesives are distinguished, asphysically setting adhesives, by the fact that application of adhesiveto one side of the bond areas, and placement of the bond areas againstone another, are sufficient to produce an adhesive bond, with heat beingintroduced before or after application. Curing takes place by cooling,and so the cure time can be made as short as desired, thereby preventingdisplacement of the microcomponents on the substrate in the course ofbonding.

Hotmelt adhesives have the advantage, furthermore, that the adhesivebond is reversible, although it can also be made irreversible by meansof an aftercure operation.

The hotmelt adhesives are applied preferably as granules of any desiredform, preferably spherical.

The incipient melting of the selected bondsites can take place locally,by means for example of the focusing heat source of laser irradiation ofthe selected bondsites, or globally, by heating of the entire substrateor microcomponent by means, for example, of a hotplate or infraredradiation.

The hotmelt adhesive can also be applied by immersing a heated orunheated, patterned surface of the substrate or microcomponent inpulverulent hotmelt adhesive.

The pulverulent hotmelt adhesive can also be applied by means of acontoured screen or a mask.

A further possibility, however, is to charge the selected bondsiteselectrostatically and to apply the pulverulent hotmelt adhesive to thepartly electrostatically charged surface of the substrate ormicrocomponent areally.

Likewise possible is the electrostatic charging of a roll from whichpulverulent hotmelt adhesives are then transferred to the substrate ormicrocomponent.

Brief heating of the surface then produces incipient melting of theadhesive at the electrostatically charged bondsites. Subsequently themicrocomponents can be placed, individually or simultaneously, on thesubstrate and adhered by heating of the assembly.

The hotmelt adhesive can also be applied by placing a transfer sheetwith granular or pulverulent adhesive attaching thereto, or a sheet ofthe hotmelt adhesive itself, onto the adherend surface of themicrocomponent or substrate. To select bondsites, the sheet ispreferably contoured. It is also possible, however, for the sheet to bemechanically stamped onto the substrate or microcomponent, or to belocally heated at selected bondsites, in order to transfer the adhesiveattaching to the sheet to the selected bondsites.

When at least one microcomponent has been adhered to the substrate it ispreferred to carry out afterheating of the system component in order toeffect an adhesive bond. This afterheating may take place selectively,by means of laser, for example, or globally.

The granules of the adhesives ought to have a diameter of less than 150μm and to be situated preferably in the range from 0.5 to 150 μm. Thesegranules may have any desired form, a sphere form for example.

The object is further achieved by the microsystem component, in whichthe adhesive bond between substrate and microcomponents is performedusing hotmelt adhesive. These microcomponents are preferably smallerthan 1000 μm.

The invention is illustrated below with reference to the attacheddrawings, in which

FIG. 1 shows an outline of the method of gluing microcomponents byapplication of a spherical hotmelt adhesive to a smooth or patternedsurface;

FIG. 2 shows an outline of the method for electrostatically charging adefined bond area;

FIG. 3 shows an outline of the method for applying a pulverulent hotmeltadhesive extensively to the substrate surface;

FIG. 4 shows an outline of a method for gluing microcomponents withextensive application of adhesive and incipient melting or sinteringselected bond areas by means of a focused heat source;

FIG. 5 shows an outline of the surface from FIG. 3 and FIG. 4 withadhesive remaining only at the bondsites as a result of electrostaticcharging, incipient melting or incipient sintering;

FIG. 6 shows an outline of a method for applying electrostaticallycharged pulverulent adhesive or dispersed hotmelt adhesive by means of aroll;

FIG. 7 shows an outline of a method for applying adhesive to selectedbondsites by immersion of a raised pattern into pulverulent adhesive ora dispersion;

FIG. 8 shows an outline of a method for applying adhesive by means ofscreen printing;

FIG. 9 shows an outline of a method for applying an adhesive by means ofa transfer tape or of a sheet produced from hotmelt adhesive;

FIG. 10 shows an outline of a method for applying adhesive with atransfer tape for contoured hotmelt adhesives;

FIG. 11 shows an outline of the method for applying adhesive to atransfer sheet or a substrate, with contoured sections of adhesive beingdeposited onto the transfer sheet or the substrate;

FIG. 12 shows an outline of the method for applying adhesive byimmersion of a microcomponent in pulverulent hotmelt adhesive or adispersion.

FIG. 1 indicates an embodiment of the method for gluing microcomponentsto a substrate 1. The substrate 1 has either a smooth surface 2 or apatterned surface with depressions 3 or elevations 4. The adhesive 5 isdeposited individually and precisely on the bond areas, in the form of agranular reactive or nonreactive hotmelt adhesive, by means of a gripper6. Particularly as a result of the patterned and/or heated surface, thegranular adhesive 5 stays in its position. The form of the granules canbe any desired form, examples being cuboidal, prism-shaped, spherical asdepicted, or irregular.

When the adhesive 5 has been applied in this way, it is heated and atleast one microcomponent is placed onto the bond areas of the substrate1 that have been provided with adhesive 5. Heating may take place evenduring application, using a preheated gripper 6. The gripper 6 used mayalso be a needle for accepting and placing the adhesive granules. Oncooling, an undisplaceable adhesive bond is produced immediately betweenmicrocomponent and substrate 1.

FIG. 2 shows another embodiment of the method for applying adhesive 5for producing microsystem components. In this case, selected bond areas7 a are electrostatically charged by means of an electrode 8. Theelectrode 8 is passed in this case over the areas 7 a where bonding isto take place, so that these areas can be easily contoured in anydesired form.

In another embodiment the electrostatic charging of the bond area 7 btakes place using a mask or electrode 9 which is adapted geometricallyto the form of the bond area 7 b.

The adhesive 5 can then be placed individually with a gripper 6, orscattered on in powder form. The electrostatic precharged surface of thesubstrate 1 can also be immersed in pulverulent adhesive 5.

As already described above, the adhesive locally applied in this way isthen heated and the at least one microcomponent is applied to thesubstrate 1.

FIG. 3 shows a method for applying a pulverulent adhesive 5 extensivelyto the surface of a substrate 1.

In a subsequent step, which is outlined in FIG. 4, the pulverulentadhesive 5 is incipiently melted or sintered at the selected bond areas7 by local heating with a focusable heat source, such as a laser beam,an infrared light beam, a UV light beam, etc., for example.Alternatively the bond areas can also be electrostatically chargedbeforehand, as shown in FIG. 2. The pulverulent adhesive 5 is thenremoved from those areas 10 of the substrate 1 where no bonding is totake place.

The incipient melting or sintering of selected bond areas 7 of thesubstrate 1 coated extensively, as outlined in FIG. 3, with pulverulentadhesive 5 can also be accomplished by masking off the areas 10 where nobonding is to take place, using a reflective mask, and extensivelyirradiating the surface of the substrate 1 with a heat source.

As shown in FIG. 5, as a result of the incipient melting or sintering,the adhesive 5 remains attached at the selected bondsites 7 and caneasily be removed from the areas 10 where no bonding is to take place.

FIG. 6 shows another embodiment of the method for applying adhesive 5 inthe form of an electrostatically charged pulverulent hotmelt adhesive ora hotmelt adhesive dispersion. In this case the adhesive 5 is applied toan electrostatically charged or contoured roll 12 which is movedrelative to the surface of the substrate 1. By this means the adhesive5, which attaches locally and in a targeted way to the surface of theroll 12, is transferred to the selected bond areas 7.

FIG. 7 shows another embodiment of the method for applying an adhesive 5to selected bondsites of a substrate 1 or microcomponent. The substrate1 or microcomponent has a raised pattern at the selected bond areas 7,and this pattern is immersed in pulverulent adhesive or a hotmeltadhesive dispersion. The raised bond areas 7 are thereby wetted withadhesive 5, and those areas 10 of the substrate 1 where no bonding is totake place remain uncoated.

FIG. 8 shows another embodiment for applying adhesive 5 in the form of apulverulent hotmelt adhesive or a dispersion of such an adhesive 5. Theadhesive 5 in this case is scattered through a contoured screen orapplied in the form of a dispersion, by means of a screen printingtechnique, using a screen 13 that has screen openings 14 correspondingto the selected bond areas 7.

FIGS. 9 to 11 show a different method of applying adhesive 5 to asubstrate 1 or microcomponent by means of a transfer sheet 15. Thetransfer sheet 15 can be moved in a way similar to a typewriter ribbonover the surface of the substrate 1. The transfer sheet 15 carries thehotmelt adhesive 5 in the form of a relatively thin layer onto thesurface which faces the substrate 1. By means of a focused heat source11, a laser for example, the sheet is heated at selected sites,corresponding to the bond areas 7, and in this way the adhesive 5 isattached to the surface of the substrate 1 at the selected bondsites 7.Alternatively, a contoured die 16 can be used to press the adhesive 5mechnically onto the surface of the substrate 1 at the selectedbondsites 5. The sheet 15, which is like a transfer tape, is movedcontinuously or discontinuously relative to the surface of the substrate1, as outlined by the arrow, so that complete areas of adhesive forapplication to the substrate 1 are always available.

FIG. 10 shows another embodiment of the application of adhesive 5 bymeans of a transfer sheet 15 to a substrate 1 and a microcomponent. Inthis case the adhesive 5 is already applied in corresponding contouredform to the transfer sheet 15 in the bond areas 7. The contouring can beaccomplished by cutting out, by means of a laser or milling cutter, forexample. The transfer sheet 15 with the contoured adhesive 5 is thenplaced on the surface of the substrate 1 and pressed on using a roll 12,so that the adhesive 5 remains attached to the surface of the substrate1.

FIG. 11 shows another embodiment, in which a contoured adhesive sheet 17is picked up with a gripper 6 and deposited in a targeted way on atransfer sheet 15. The transfer sheet 15 can then be applied to thesubstrate 1 in the manner shown in FIG. 10. Alternatively, as outlinedin FIG. 11, the contoured adhesive sheet 17 can be deposited directly onthe substrate 1 at the selected bond areas 7.

The gripper 6 may be a suction gripper, an electrostatically chargedgripper, a mechanical gripper, a needle, etc.

The adhesive 5 may be applied not only to the surface of the substrate1, as outlined, but instead, correspondingly, to the microcomponents, orboth to the substrate 1 and to the microcomponents.

In this case, as outlined in FIG. 12, the microcomponent 18 can begripped with a gripper 6 and immersed in a vessel containing adispersion of a hotmelt adhesive or of a pulverulent hotmelt adhesive.It is advantageous in this case if the microcomponent 18 has beenheated.

1. A method for gluing microcomponents to a substrate in the productionof microsystem components, comprising the following steps: applying areactive or nonreactive hotmelt adhesive to at least one microcomponentand/or the substrate; heating the hotmelt adhesive, and applying the atleast one microcomponent to the substrate, the hotmelt adhesive being onthe contact areas between the at least one microcomponent and thesubstrate, wherein said applying step includes areal application ofpulverulent hotmelt adhesive to a surface of the substrate or the atleast one microcomponent, incipient melting of selected bond sites bylocal heating by means of irradiation of the selected bondsites througha focusable heat source of a powder layer; removal of the powder layernot incipiently melted; and adhesion of the at least one microcomponentto the substrate.
 2. The method of claim 1, wherein said heating takesplace selectively with a focusing heat source.
 3. The method of claim 1wherein the hotmelt adhesive is applied as granules.
 4. The method ofclaim 1 wherein the incipient melting takes place with a laser.
 5. Themethod of claim 1 further comprising the step of immersing a heatedsubstrate or microcomponent in pulverulent hotmelt adhesive to apply theadhesive at the immersed areas.
 6. The method of claim 1 wherein saidapplying step includes application of pulverulent hotmelt adhesivethrough a contoured screen to the substrate or the at least onemicrocomponent
 1. 7. The method of claim 1 further comprising the stepof electrostatic charging of a surface and/or a pulverulent hotmeltadhesive to support the areal or patterned application of adhesive. 8.The method of claim 1 further comprising the step of immersion of aheated patterned surface of the substrate or the at least onemicrocomponent in pulverulent hotmelt adhesive to apply the adhesive atraised sites on the patterned surface.
 9. The method claim 1 furthercomprising the steps of electrostatic charging of a roll, and whereinareal application of the pulverulent hotmelt adhesive is made to apartly electrostatically charged surface of the roll, and transferringselected bondsites from the roll to the substrate or the at least onemicrocomponent, and wherein brief heating of the surface is used toincipiently melt the adhesive.
 10. The method of claim 1 furthercomprising the step of electrostatic charging of the selected bondsites,and wherein areal application of the pulverulent hotmelt adhesive isperformed to a partly electrostatically charged surface of the substrateor the at least one microcomponent, and brief heating of the surface isperformed to incipiently melt the adhesive at the electrostaticallycharged bondsites.
 11. The method of claim 1, further comprisingplacement of a transfer sheet with granular or pulverulent adhesiveattaching thereto, or of a layer produced from hotmelt adhesive, to theadherend surface of the at least one microcomponent or substrate. 12.The method of claim 11, further comprising the step of contouring of thetransfer sheet to select bondsites.
 13. The method of claim 11,characterized by application of the adhesive to selected bondsites, whenthe transfer sheet lies on the surface of at least one microcomponent orsubstrate, by mechanically stamping the transfer sheet onto thesubstrate or the at least one microcomponent or locally heating thetransfer sheet.
 14. The method of claim 1 further comprising the step ofpreheating of at least surfaces to which adhesive is applied.
 15. Themethod of claim 1 further comprising the step of afterheating of the atleast one microsystem component after adhering to the substrate.
 16. Themethod of claim 14, wherein afterheating takes place selectively bymeans of focusing heat source or globally.
 17. The method of claim 1wherein the granules of the adhesives shave a diameter of less than 150μm.
 18. The method of claim 17, characterized in that the diameter ofthe granules is situated in the range from 0.5 to 150 μm.
 19. Amicrosystem component having at least one microcomponent bonded to asubstrate, characterized in that the adhesive bonding is performed bythe method of applying a reactive or nonreactive hotmelt adhesive to atleast one microcomponent and/or the substrate, heating the hotmeltadhesive, and applying the at least one microcomponent to the substrate,the hotmelt adhesive being on the contact areas between the at least onemicrocomponent and the substrate, wherein said applying step includesareal application of pulverulent hotmelt adhesive to a surface of thesubstrate or the at least one microcomponent, incipient melting ofselected bond sites by local heating by means of irradiation of theselected bondsites through a focusable heat source of a powder layer.removal of the powder layer not incipiently melted; and adhesion of theat least one microcomponent to the substrate.
 20. The microsystemcomponent of claim 19, characterized in that the at least onemicrocomponent is smaller than 1000 μm.